The invention relates to a receiver for radio or television signals, which is provided with a high-frequency circuit comprising a discrete semiconductor component which includes a planar variable capacitance diode and an integrated series resistor on a common semiconductor substrate.
The signals emitted by a transmitter as electromagnetic high-frequency waves are received by a receiver for radio or television signals, which signals are converted by the reception antenna into high-frequency alternating voltages. A receiver separates a desired transmitter from undesired transmitters (tuning), recovers the transferred information from the modulated high-frequency oscillations (demodulation) and converts the low-frequency signals into acoustic and optical signals by means of a low-frequency amplifier.
In state-of-the-art receivers for radio or television signals, all tuning and band-switching operations are carried out electronically. For this purpose, use is made of high-frequency circuits with resonant circuits wherein variable capacitance diodes operate as variable capacitors. The tuning precision is higher as the number of tuning circuits in the receiver is larger.
The high-frequency circuits for a radio or television signal receiver may be composed of discrete components. When these discrete components are connected to leads, however, problems with the stray capacitances of the leads occur, which may have a negative effect on the tuning properties of the receiver. In order to circumvent these problems, it is disclosed in DE 39 43 013 C2 to provide a television tuner with an input stage comprising a diode consisting of a semiconductor substrate (N) and a semiconductor region (P) having opposite conductivity types, the semiconductor region being inserted into the substrate, and a resistor arranged on the substrate (N) above an insulating layer, which resistor contacts the substrate via an opening formed in the insulating layer and serves to protect the diode against excess voltages, and first and second connection elements connected to the terminals of the diode, a third connection element connected to the resistor, and a resin packing wherein the diode, the resistor and the connection elements are cast and fixed.
As a receiver for radio or television signals should convert the high-frequency input signals, which are error-ridden as a result of superimposed noise, into an error-free data stream, it is desirable that parasitic capacitances in the receiver are precluded as much as possible.
Therefore, it is an object of the invention to provide a radio or television signal receiver with reduced parasitic capacitances and an improved data reception.
In accordance with the invention, this object is achieved by a receiver for radio or television signals provided with a high-frequency circuit comprising a discrete semiconductor component, which includes a planar variable capacitance diode formed on a semiconductor substrate 4 of a first doping type with a first doping density n1, on which semiconductor substrate an epitaxial layer 3 of the same doping type with a second doping density n2 greater than n1 is provided, on which epitaxial layer an insulation layer 5 having a first window is provided by means of a first laterally bounded semiconductor region 2 of a second doping type with a doping density n3 greater than n2 in the epitaxial layer below the first window, and a first contact pad 6 which contacts the first laterally bounded semiconductor region via the first window, which semiconductor component further includes an integrated series resistor composed of a resistor path 8 which comprises two path ends on the insulation layer, the first path end being in contact, through a second window in the insulation layer, with a third laterally bounded semiconductor region 9 of the first doping type with a doping density n5 greater than n2, which extends, in the vertical direction, at least through the epitaxial layer, which resistor path further comprises a second contact pad 7, which is arranged on the insulation layer and contacts the second path end of the resistor path, and a second laterally bounded semiconductor region 1 in the epitaxial layer, below the second contact pad and the resistor path, said semiconductor region having a doping of the second doping type with a doping density n4, which substantially compensates for the doping of the first doping type with a doping density n2 of the epitaxial layer.
By providing the epitaxial layer with an additional doping below the second contact pad and the resistor path, the parasitic capacitances are reduced at said location. A reduction of the parasitic capacitance results in an increase of the Q factor of the variable capacitance diode and hence also an increase of the circuit performance. The overall circuit loss is reduced.
The invention also relates to a discrete semiconductor component which comprises a planar variable capacitance diode formed on a semiconductor substrate of a first doping type with a first doping density n1, on which semiconductor substrate an epitaxial layer of the same doping type with a second doping density n2 greater than n1 is provided, on which epitaxial layer an insulation layer having a first window is provided by means of a first laterally bounded semiconductor region of a second doping type with a doping density n3 greater than n2 in the epitaxial layer below the first window, and a first contact pad which contacts the first laterally bounded semiconductor region via the first window, which semiconductor component further comprises an integrated series resistor composed of a resistor path having two path ends on the insulation layer, the first path end being in contact, through a second window in the insulation layer, with a third laterally bounded semiconductor region of the first doping type with a doping density n5 greater than n2, which extends, in the vertical direction, at least through the epitaxial layer, which resistor path further comprises a second contact pad, which is arranged on the insulation layer and contacts the second path end of the resistor path, and a second laterally bounded semiconductor region in the epitaxial layer, below the second contact pad and the resistor path, said semiconductor region having a doping of the second doping type with a doping density n4, which substantially compensates for the doping of the first doping type with a doping density n2 of the epitaxial layer.
A reduction of the parasitic capacitances results in a reduction of the associated substrate losses and RC propagation delays. This is advantageous, particularly at high frequencies occurring, for example, in cordless RF communication applications and digital high-velocity applications.
Within the scope of the invention it may be preferred that the sum of the charge carrier concentration n4 and n2 is below 1016/cm3.
Particularly advantageously, the second laterally bounded semiconductor region extends across the entire thickness of the epitaxial layer.
It may also be preferred for the doping density n4 of the second laterally bounded semiconductor region to decrease from the boundary surface to the insulation layer to the boundary surface to the substrate.
In accordance with a further preferred embodiment of the invention, the semiconductor substrate comprises a rear-side metallization.
In accordance with a particularly preferred embodiment of the invention, the discrete semiconductor component is accommodated in a standardized transistor housing having three connections. The signal paths in the accommodated semiconductor component are short, thus rendering it particularly suitable for use in the high-frequency range. In comparison with the prior art, the process and manufacturing costs of the receiver comprising a semiconductor component with a standardized housing are reduced, which can be attributed to the small surface space required and to a smaller number of loading operations.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.